The average of 5 numbers is 8. The average of two of the numbers is -6, what is the sum of the 3 other numbers?

If the average of 5 numbers is 8, their sum must be 40.

And if the average of two of them is -6, their sum must be -12.

So, the sum of the other three numbers is 40 - (-12) = 40 + 12  = 52.